Rf receiver and digitally-assisted calibration method applicable thereto

ABSTRACT

A radio frequency (RF) receiver includes a digital tuning engine; I-path and Q-path analog filters, tuned by the digital tuning engine; and a digital compensation circuit. The digital tuning engine executes a RC (resistor-capacitor) time constant calibration to adjust respective cut-off frequencies of the I-path analog filter and the Q-path analog filter. The digital tuning engine executes a filter mismatch calibration to match the I-path analog filter and the Q-path analog filter. The digital tuning engine executes a filter residual mismatch calibration to match an I-path response from the I-path analog filter to the digital compensation circuit and a Q-path response from the Q-path analog filter to the digital compensation circuit.

This application claims the benefit of U.S. provisional application Ser.No. 61/622,317, filed Apr. 10, 2012, the subject matter of which isincorporated herein by reference.

TECHNICAL FIELD

The disclosure relates in general to a radio frequency (RF) receiver anda digitally-assisted calibration method applicable thereto.

BACKGROUND

Radio frequency (RF) system is widely adopted in wireless communication.RF system includes at least one RF receiver and at least one RFtransmitter. RF receivers are typically designed to operate in a givenbandwidth resource. Analog and digital baseband (ADBB) receivers usuallyoperate on signals occupying a subset of the RF receiver operatingbandwidth. Such a subset is called a channel.

RF transmitter may interfere with operations of the RF receiver eventhough the RF transmitter's frequency spectrum does not overlap the RFreceiver's channel frequency spectrum. Out-of-channel interferences,especially nearby interference, may cause severe damage to ADBBreceivers (e.g. desensitization, cross-modulation, inter-modulation,saturation, synchronization error, and channel equalization error).

A lot of implementations have been proposed to suppress nearbyinterferences and/or out-of-channel interferences striking a RFreceiver. Analog baseband channel selection filter is a common way toremove nearby (out-of-channel) interferences.

Interference attenuation is determined by the type, order, and cut-offfrequency of a filter. If the cut-off frequency of the filter is shiftedtoward in-band due to filter variations (which may be caused by processvariability), in-band signal is hurt. On the contrary, if the cut-offfrequency of the filter is shifted toward out-band due to filtervariations, interference attenuation decreases.

Mismatch between I-path and Q-path analog filters (I referring to“in-phase” and Q referring to “quadrature-phase”) causesfrequency-dependent I/Q imbalance, which induces undesired images forquadrature RF receivers.

Analog filters should thus preserve the cut-off frequency and good matchbetween I and Q path analog filters even under process variability.

As for now, there are three kinds of variations for RC-based filter,process variation, random mismatch variation and systematic mismatchvariation (gradient effects).

As for process variations, what are considered are the variations of theprocess, not only of all chips on the same single wafer, but also thevariations on different wafers, and even on different lots. Same processvariation is assumed for components, such as resistors, capacitors, ortransistors, in a chip. Process variation significantly causes cut-offfrequency shift from the ideal one and thus injures in-band signal orreduces attenuation of interferences. However, the process variationdoes not induce frequency-dependent I/Q imbalance since this processvariation is the same in the whole chip. RC calibration is used tocompensate the process variation.

As for random mismatch variation, what is considered is the randomportion of the total mismatch of components, which are located close toeach other and which should be matched as closely as possible. Randommismatch variation is stochastic and hence cannot be predicted. Randommismatch variation slightly causes cut-off frequency shift from theideal one and introduces frequency-dependent I/Q imbalance since randommismatch variation is different for I/Q filters. Random mismatchvariation can be limited to a reasonable range by properly enlargingcomponent area, a trade off between performance and area cost.

As for systematic mismatch variation, what is considered is the portionof the total mismatch of components, which are located close to eachother and which should be matched as closely as possible, where adeterministic trend can be observed in the mismatch values of thevarious components. Systematic mismatch variation may be preciselypredicted if given the process gradient. Systematic mismatch variationmildly causes cut-off frequency shift from the ideal one. Systematicmismatch variation introduces frequency-dependent I/Q imbalance sincesystematic mismatch variation is different for I/Q filters.

Thus, it needs a compensation method which compensates mismatchpartially in the analog domain and partially in the digital domain forcost-effective designs.

SUMMARY

According to one embodiment, provided is a radio frequency (RF)receiver. The RF receiver includes a digital tuning engine; I-path andQ-path analog filters, tuned by the digital tuning engine; and a digitalcompensation circuit. The digital tuning engine executes a RC(resistor-capacitor) time constant calibration to adjust respectivecut-off frequencies of the I-path analog filter and the Q-path analogfilter. The digital tuning engine executes a filter mismatch calibrationto match the I-path analog filter and the Q-path analog filter. Thedigital tuning engine executes a filter residual mismatch calibration tomatch an I-path response from the I-path analog filter to the digitalcompensation circuit and a Q-path response from the Q-path analog filterto the digital compensation circuit.

According to another embodiment, provided is a digitally-assistedcalibration method applicable to a radio frequency (RF) receiverincluding an I (in-phase)-path analog filter, a Q(quadrature-phase)-path analog filter and a digital compensationcircuit. A RC (resistor-capacitor) time constant calibration is executedto adjust respective cut-off frequencies of the I-path analog filter andthe Q-path analog filter. A filter mismatch calibration is executed tomatch the I-path analog filter and the Q-path analog filter. A filterresidual mismatch calibration is executed to match an I-path responsefrom the I-path analog filter to the digital compensation circuit and aQ-path response from the Q-path analog filter to the digitalcompensation circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 which shows a RF receiver according to one embodiment of thedisclosure.

FIG. 2 shows a capacitor bank according to the embodiment of theapplication.

FIG. 3 shows a calibration flow disclosed in the embodiment of theapplication.

FIG. 4A shows a result of RC time constant calibration in the embodimentof the application.

FIG. 4B shows a result of I/Q filter mismatch calibration in theembodiment of the application.

FIG. 4C shows a result of filter residual mismatch calibration in theembodiment of the application.

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare schematically shown in order to simplify the drawing.

DETAILED DESCRIPTION

Although process variation doesn't induce frequency-dependent I/Qimbalance, random mismatch variation and systematic mismatch variationdo introduce frequency-dependent I/Q imbalance. Random mismatchvariation may be limited to a reasonable range by enlarging componentarea properly. So, the embodiment reduces systematic mismatch variation(gradient effect) in the RF/analog circuit design phase and further usesdigitally-assisted calibration to reduce impact on I/Q imbalance causedby systematic mismatch variation.

Besides, as for relationship between I/Q filter mismatch and I/Qimbalance, gain imbalances and phase imbalances near DC frequency may besmall even under severe filter mismatch. Gain imbalances or phaseimbalances near cut-off frequency or a certain frequency become abruptlysignificant; and in the embodiment of the disclosure, this may be anindicator to detect I/Q filter mismatch.

Referring to FIG. 1 which shows a RF receiver according to oneembodiment of the disclosure. As shown in FIG. 1, the RF receiver 100includes an antenna 110, an amplifier 120, an I-path mixer 130A, aQ-path mixer 130B, an I-path analog filter 140A, a Q-path analog filter140B, a digital tuning engine 150 and a digital compensation circuit160.

The antenna 110 receives RF signals from, for example, RF transmitters(not shown) and sends the received RF signals to the amplifier 120.

The I-path mixer 130A mixes the amplified RF signals from the amplifier120 with a local reference signal LO_(I). The mixture signals from theI-path mixer 130A are sent to the I-path analog filter 140A. Similarly,the Q-path mixer 130B mixes the amplified RF signals from the amplifier120 with a local reference signal LO_(Q). The mixture signals from theQ-path mixer 130B are sent to the Q-path analog filter 140B.

The I-path analog filter 140A includes an analog filter 141A and ananalog-digital converter (ADC) 142A. Similarly, the Q-path analog filter140B includes an analog filter 141B and an analog-digital converter(ADC) 142B. The I-path analog filter 140A and the Q-path analog filter140B are coupled to and tuned by the digital tuning engine 150.

The digital tuning engine 150 executes a RC (resistor-capacitor) timeconstant calibration to adjust respective cut-off frequencies of theI-path analog filter 140A and the Q-path analog filter 140B. Further,the digital tuning engine 150 executes a filter mismatch calibration tomatch the I-path analog filter 140A and the Q-path analog filter 140B.The digital tuning engine 150 executes a filter residual mismatchcalibration to match an I-path response from the I-path analog filter140A to the digital compensation circuit 160 and a Q-path response fromthe Q-path analog filter 140B to the digital compensation circuit 160.Details of the operations of the digital tuning engine 150 are describedin the following.

When the digital tuning engine 150 performs the filter residual mismatchcalibration as mentioned above, the digital tuning engine 150 mayfurther concurrently perform a mismatch calibration on the I/Q imbalancehappened before the analog filters 140A and 140B, for example,calibrating the I/Q imbalance of the I-path mixer 130A and/or the Q-pathmixer 130B. In fact, signals used in the filter residual mismatchcalibration pass through the I-path mixer 130A and the Q-path mixer 130Bbefore they arrive at the analog filters 140A and 140B. If I/Q imbalanceof the I-path mixer 130A and the Q-path mixer 130B has not fullycompensated yet, then in the embodiment, during filter residual mismatchcalibration, I/Q imbalance of the I-path mixer 130A and the Q-path mixer130B may be also removed by the digital tuning engine 150, as long asthe I-path analog filter 140A and the Q-path analog filter 140B haveenough capability of I/Q mismatch compensation.

The digital compensation circuit 160 is coupled to the digital tuningengine 150, the I-path analog filter 140A and the Q-path analog filter140B.

The analog filter 141A of the I-path analog filter 140A includes aplurality of capacitors each including a capacitor bank. The capacitorbank is tuned by the digital tuning engine. Now, please refer to FIG. 2,which shows a capacitor bank according to the embodiment of theapplication. As shown in FIG. 2, the capacitor bank includes a pluralityof parallel sub-capacitors C₀˜C_(N) and a plurality of parallel switchesSW₁˜SW_(N). The switches SW₁˜SW_(N) is coupled to a corresponding one ofthe sub-capacitors C₀˜C_(N). The digital tuning engine 150 controlssetting of the capacitor bank by turning on/off of the switchesSW₁˜SW_(N) of the capacitor bank. That is, the digital tuning engine 150varies the total effective capacitance of the capacitor bank by turningon/off switches SW₁˜SW_(N). Connection/disconnection of switches willhave an influence on the total effective capacitance value of thecapacitor bank. So, the total effective capacitance of the capacitorbank has a minimum value of C₀ and a maximum value of

$C_{0} + {\sum\limits_{i = {1\sim N}}{C_{i}.}}$

The structure of the capacitor banks of each capacitor in the Q-pathanalog filter 140B is the same or similar to that of the I-path analogfilter 140A, and thus details are omitted here.

Now, please refer to FIG. 3 for explaining the calibration flowdisclosed in the embodiment of the application. In the embodiment of theapplication, three kinds of calibration are performed, i.e. RC(resistor-capacitor) time constant calibration (for adjusting respectivecut-off frequencies of the I-path analog filter 140A and the Q-pathanalog filter 140B), I/Q filter mismatch calibration (for matching theI-path analog filter 140A and the Q-path analog filter 140B) and I/Qfilter residual mismatch calibration (for matching I-path response andQ-path response).

In executing RC time constant calibration in step 310, the digitaltuning engine 150 adjusts the filter cut-off frequencies of the I-pathanalog filter 140A and the Q-path analog filter 140B by turning ON/OFFthe capacitors.

Operation principle of RC time constant calibration is for example butnot limited by as follows. The capacitance of the capacitor bank isreset (for example, all switches are disconnected so that the totalcapacitance of the capacitor bank has a minimum value C₀). The capacitorbank is charged for a fixed time. An integrator output (for example,from the ADC) is compared with a threshold voltage. The capacitor bankis adjusted (that is, the switches SW₁˜SW_(N) are turned ON/OFF)successively to change the capacitance value of the capacitor bank tomake the integrator output equal to the threshold voltage.

In the embodiments, the digital tuning engine has several ways tocontrol the capacitance of the capacitor bank.

One implementation for controlling the capacitance of the capacitor bankis as follows. In executing the RC time constant calibration, thedigital tuning engine 150 gets a capacitor bank setting by performing RCtime constant calibration on one of the capacitors of either the I-pathanalog filter 140A or the Q-path analog filter 140B. Then, the digitaltuning engine 150 tunes/controls all of the capacitors of both theI-path analog filter 140A and the Q-path analog filter 140B based on thecapacitor bank setting. For example, all capacitor banks of both theI-path analog filter 140A and the Q-path analog filter 140B are setbased on the capacitor bank setting.

Another implementation for controlling the capacitance of the capacitorbank is as follows. In executing the RC time constant calibration, thedigital tuning engine 150 gets an I-path capacitor bank setting byperforming RC time constant calibration on one of the capacitors of theI-path analog filter 140A; and the digital tuning engine 150tunes/controls all of the capacitors of the I-path analog filter basedon the I-path capacitor bank setting. For example, all capacitor banksof the I-path analog filter 140A are set based on the I-path capacitorbank setting.

Still another implementation for controlling the capacitance of thecapacitor bank is as follows. In executing the RC time constantcalibration, the digital tuning engine 150 gets a Q-path capacitor banksetting by performing RC time constant calibration on one of thecapacitors of the Q-path analog filter 140B; and the digital tuningengine 150 tunes/controls all of the capacitors of the Q-path analogfilter 140B based on the Q-path capacitor bank setting. For example, allcapacitor banks of the Q-path analog filter 140B are set based on theQ-path capacitor bank setting.

FIG. 4A shows a result of RC time constant calibration in the embodimentof the application. As shown in FIG. 4A, H(f), H_(I)(f) and H_(Q)(f)refers to a target response, an I-path response and a Q-path response.After RC time constant calibration, the I-path response H_(I)(f) and theQ-path response H_(Q)(f) are pushed or pulled closer to the targetresponse H(f) than before RC time constant calibration. But, mismatchbetween the I-path response H_(I)(f) and the Q-path response H_(Q)(f)are not calibrated by the RC time constant calibration.

In step 320, I/Q filter mismatch calibration is performed. In executingthe filter mismatch calibration, the digital tuning engine 150 gets I/Qgain and phase imbalances at two distinct frequencies to mach the I-pathanalog filter 140A and the Q-path analog filter 140B. Further, thedigital tuning engine 150 has several implementations to execute I/Qfilter mismatch calibration.

In one implementation to execute I/Q filter mismatch calibration, a RFtransmitter (not shown) transmits a first tone at an in-band frequencyto the mixers 130A and 130B to get the gain and phase imbalance atin-band frequency, which includes mixer and filter mismatches. Indetails, in response to the first tone at the in-band frequency receivedby the mixers 130A and 130B, the digital tuning engine 150 gets a firstI/Q gain imbalance and a first I/Q phase imbalance at the in-bandfrequency. Then, the RF transmitter transmits a second tone at anear-cut-off frequency or at a certain frequency to the mixers 130A and130B to get the gain and phase imbalance near cut-off frequency or at acertain frequency, which includes mixer and filter mismatches. Inresponse to the second tone received by the mixers 130A and 130B, thedigital tuning engine 150 gets a second I/Q gain imbalance and a secondI/Q phase imbalance at the near-cut-off frequency or at the certainfrequency. The digital tuning engine 150 tunes settings of the capacitorbanks of the I-path analog filter 140A and/or the Q-path analog filter140B based on a first difference D1 between the first I/Q gain imbalanceand the second I/Q gain imbalance. The digital tuning engine 150 tunessettings of the capacitor banks of the I-path analog filter 140A and/orthe Q-path analog filter 140B based on a second difference D2 betweenthe first I/Q phase imbalance and the second I/Q phase imbalance. Inmore details, if a condition is met (D1≧THRESHOLD_g orD1≦(−1*THRESHOLD_g)), then the digital tuning engine 150 tunes settingsof the capacitor banks of the I-path analog filter 140A and/or theQ-path analog filter 140B. THRESHOLD_g is a threshold value.Alternatively, if another condition is met (D2≧THRESHOLD_p orD2≦(−1*THRESHOLD_p)), then the digital tuning engine 150 tunes settingsof the capacitor banks of the I-path analog filter 140A and/or theQ-path analog filter 140B. THRESHOLD_p is a threshold value.Alternatively, if both the two conditions are met, then the digitaltuning engine 150 tunes settings of the capacitor banks of the I-pathanalog filter 140A and/or the Q-path analog filter 140B.

In another implementation to execute I/Q filter mismatch calibration,the RF transmitter transmits a plurality of tones to the mixers 130A and130B. At least one of the tones is at the in-band frequency, called athird tone, to get the gain and phase imbalance at in-band frequency,which includes mixer and filter mismatches; and at least one of thetones is at the near-cut-off frequency or at the certain frequency,called the fourth tone, to get the gain and phase imbalance at thenear-cut-off frequency or at the certain frequency, which includes mixerand filter mismatches. The digital tuning engine 150 gets a third I/Qgain imbalance and a third I/Q phase imbalance at the in-band frequency;and the digital tuning engine 150 gets a fourth I/Q gain imbalance and afourth I/Q phase imbalance at the near-cut-off frequency or at thecertain frequency. The digital tuning engine 150 tunes settings of thecapacitor banks of the I-path analog filter 140 a and/or the Q-pathanalog filter 140B based on a third difference D3 between the third I/Qgain imbalance and the fourth I/Q gain imbalance. The digital tuningengine 150 tunes settings of the capacitor banks of the I-path analogfilter 140A and/or the Q-path analog filter 140B based on a fourthdifference D4 between the third I/Q phase imbalance and the fourth I/Qphase imbalance. In more details, if a condition is met (D3≧THRESHOLD_gor D3≦(−1*THRESHOLD_g)), then the digital tuning engine 150 tunessettings of the capacitor banks of the I-path analog filter 140A and/orthe Q-path analog filter 140B. Alternatively, if another condition ismet (D4≧THRESHOLD_p or D4≦(−1*THRESHOLD_p)), then the digital tuningengine 150 tunes settings of the capacitor banks of the I-path analogfilter 140A and/or the Q-path analog filter 140B. Alternatively, if boththe two conditions are met, then the digital tuning engine 150 tunessettings of the capacitor banks of the I-path analog filter 140A and/orthe Q-path analog filter 140B.

In still another implementation to execute I/Q filter mismatchcalibration, the RF transmitter transmits a fifth tone at the in-bandfrequency directly to the I-path analog filter 140A and Q-path analogfilter 140B to get the gain and phase imbalance at in-band frequency,which includes filter mismatches. Further, the RF transmitter transmitsa sixth tone at the near-cut-off frequency or at the certain frequencydirectly to the I-path analog filter 140A and Q-path analog filter 140Bto get the gain and phase imbalance at in-band frequency, which includesfilter mismatches. In this implementation, because the tones aredirectly transmitted to the I-path analog filter 140A and Q-path analogfilter 140B (i.e. the tone does not pass through the mixers 130A and130B), the gain and phase imbalance does not include mixer mismatches.In response to the fifth tone directly received by the I-path analogfilter 140A and the Q-path analog filter 140B, the digital tuning engine150 gets a fifth I/Q gain imbalance and a fifth I/Q phase imbalance atthe in-band frequency. Further, in response to the sixth tone directlyreceived by the I-path analog filter 140A and the Q-path analog filter140B, the digital tuning engine 150 gets a sixth I/Q gain imbalance anda sixth I/Q phase imbalance at the near-cut-off frequency or at thecertain frequency. The digital tuning engine 150 tunes settings of thecapacitor banks of the I-path analog filter 140A and/or the Q-pathanalog filter 140B based on a fifth difference D5 between the fifth I/Qgain imbalance and the sixth I/Q gain imbalance. The digital tuningengine 150 tunes settings of the capacitor banks of the I-path analogfilter 140A and/or the Q-path analog filter 140B based on a sixthdifference D6 between the fifth I/Q phase imbalance and the sixth I/Qphase imbalance. In more details, if a condition is met (D5≧THRESHOLD_gor D5≦(−1*THRESHOLD_g)), then the digital tuning engine 150 tunessettings of the capacitor banks of the I-path analog filter 140A and/orthe Q-path analog filter 140B. Alternatively, if another condition ismet (D6≧THRESHOLD_p or D6≦(−1*THRESHOLD_p)), then the digital tuningengine 150 tunes settings of the capacitor banks of the I-path analogfilter 140A and/or the Q-path analog filter 140B. Alternatively, if boththe two conditions are met, then the digital tuning engine 150 tunessettings of the capacitor banks of the I-path analog filter 140A and/orthe Q-path analog filter 140B.

In yet another implementation to execute I/Q filter mismatchcalibration, the RF transmitter transmits a plurality of tones directlyto the I-path analog filter 140A and Q-path analog filter 140B (i.e. thetone does not pass through the mixers 130A and 130B). At least one oftones is at the in-band frequency, called the seventh tone, to get thegain and phase imbalance at in-band frequency, which includes filtermismatches; and at least one of the ones is at the near-cut-offfrequency or at the certain frequency directly, called the eighth tone,to get the gain and phase imbalance at the near-cut-off frequency or atthe certain frequency, which includes filter mismatches. In response tothe seventh tone directly received by the I-path analog filter 140A andthe Q-path analog filter 140B, the digital tuning engine 150 gets aseventh I/Q gain imbalance and a seventh I/Q phase imbalance at thein-band frequency. In response to the eighth tone directly received bythe I-path analog filter 140A and the Q-path analog filter 140B, thedigital tuning engine 150 gets an eighth I/Q gain imbalance and aneighth I/Q phase imbalance at the near-cut-off frequency or at thecertain frequency. The digital tuning engine 150 tunes settings of thecapacitor banks of the I-path analog filter 140A and/or the Q-pathanalog filter 140B based on a seventh difference D7 between the seventhI/Q gain imbalance and the eighth I/Q gain imbalance. The digital tuningengine 150 tunes settings of the capacitor banks of the I-path analogfilter 140A and/or the Q-path analog filter 140B based on an eighthdifference D8 between the seventh I/Q phase imbalance and the eighth I/Qphase imbalance. In more details, if a condition is met (D7≧THRESHOLD_gor D7≦(−1*THRESHOLD_g)), then the digital tuning engine 150 tunessettings of the capacitor banks of the I-path analog filter 140A and/orthe Q-path analog filter 140B. Alternatively, if another condition ismet (D8≧THRESHOLD_p or D8≦(−1*THRESHOLD_p)), then the digital tuningengine 150 tunes settings of the capacitor banks of the I-path analogfilter 140A and/or the Q-path analog filter 140B. Alternatively, if boththe two conditions are met, then the digital tuning engine 150 tunessettings of the capacitor banks of the I-path analog filter 140A and/orthe Q-path analog filter 140B.

Now, please refer to FIG. 4B, which shows a result of I/Q filtermismatch calibration in the embodiment of the application. As shown inFIG. 4B, after I/Q filter mismatch calibration, the filter mismatchbetween the I-path response H_(I)(f) and the Q-path response H_(Q)(f) issmaller than before I/Q filter mismatch calibration.

In step 330, the digital tuning engine 150 executes a filter residualmismatch calibration to more match the I-path response H_(I)(f) with theQ-path response H_(Q)(f). FIG. 4C shows a result of filter residualmismatch calibration in the embodiment of the application. As shown inFIG. 4C, after I/Q filter residual mismatch calibration, the filtermismatch between the I-path response H_(I)(f) and the Q-path responseH_(Q)(f) is even smaller than before I/Q filter residual mismatchcalibration. For example, after I/Q filter residual mismatchcalibration, the calibrated I-path response H_(I)′(f) from the digitalcompensation circuit 160 is the same as the I-path response H_(I)(f)(i.e. H_(I)′(f). H_(I)(f)) but the calibrated Q-path response H_(Q)′(f)from the digital compensation circuit 160 is the same as the calibratedI-path response H_(I)′(f) (i.e. H_(Q)′(f)=H_(I)′(f)).

In summary, in the embodiment of the application, in order to calibratesystematic mismatch variations, detection of frequency-dependent I/Qimbalance is provided, in order to reduce I/Q filter mismatch due togradient effects, which improves I/Q filter imbalances.Frequency-dependent I/Q imbalance measurement is to detect I/Q filtermismatch. Measurement of I/Q imbalance on at least two frequencies (forexample, at the in-band frequency, or near cut-off frequency or at thedesired frequency) is to detect I/Q filter mismatch. Based on results ofmismatch detection, the embodiment finely tunes capacitor bank settingof I-path analog filter and/or Q-path analog filter, to reducesystematic mismatch variations. For the capacitor bank tuning, the samesetting is applied to each stage of I-path analog filter and/or Q-pathanalog filter when the 1st-order gradient effect dominates thesystematic mismatch to reduce calibration complexity. For the capacitorbank tuning, stage-by-stage calibration is applied for the generalcases, where higher-order gradient effects exists in addition to1st-order gradient effect.

Still further, in the embodiment, in order to calibrate random mismatchvariation, detection of frequency-dependent I/Q imbalance is provided inorder to reduce I/Q filter mismatch, which improves I/Q filterimbalances. Frequency-dependent I/Q imbalance measurement is to detectI/Q filter mismatch. Measurement of I/Q imbalance on at least twofrequencies is to detect I/Q filter mismatch. Based on results ofmismatch detection, the embodiment finely tunes capacitor bank settingof I-path analog filter and/or Q-path analog filter to reduce randommismatch variations. For the capacitor bank tuning, stage-by-stagecalibration is applied to reduce the random mismatch variations.

Still further, in the embodiment, a complete digitally-assistedcalibration flow for filter variations, which include processvariations, systematic mismatch variations, and random mismatchvariations, is provided to adjust cut-off frequency of I-path analogfilter and Q-path analog filter to the desired frequency and to alignI/Q filter systematic and random mismatches in order to improve filterattenuation and I/Q imbalance. RC calibration is to deal with processvariations. Frequency-dependent I/Q imbalance detection is to deal withsystematic variations and random mismatch variations. Digitalfrequency-dependent I/Q calibration is to deal with residual systematicvariations and random mismatch variations.

Effects and advantages of the embodiment are as follows.

The I-path analog filter 140A and the Q-path analog filter 140B are inanalog domain while the digital tuning engine 150 and the digitalcompensation circuit 160 are in digital domain. In the embodiment, thesystematic mismatch variation and random mismatch variation arecalibrated in the analog domain so that the tap number of digitalcompensation filter will be reduced significantly. Thus, the powerconsumption in the digital domain is reduced without adding powerconsumption in the analog domain.

Also, the embodiment is suitable in high-performance receiver. Asdiscussed above, in the prior art, in order to limit the random mismatchvariation, the circuit component area should be enlarged or otherwise itneeds digital compensation filter for I/Q imbalance. However, in theembodiment, the random mismatch variation and systematic mismatchvariation are calibrated to compensate filter mismatch in the analogdomain through the capacitor bank tuning. Thus, there is no need fordigital compensation filter if I/Q imbalance of the residual systematicvariation and the random mismatch variation is small enough.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodiments.It is intended that the specification and examples be considered asexemplary only, with a true scope of the disclosure being indicated bythe following claims and their equivalents.

What is claimed is:
 1. A radio frequency (RF) receiver, comprising: adigital tuning engine; an I (in-phase)-path analog filter, coupled toand tuned by the digital tuning engine; a Q (quadrature-phase)-pathanalog filter, coupled to and tuned by the digital tuning engine; and adigital compensation circuit, coupled to the digital tuning engine, theI-path analog filter and the Q-path analog filter; wherein the digitaltuning engine executes a RC (resistor-capacitor) time constantcalibration to adjust respective cut-off frequencies of the I-pathanalog filter and the Q-path analog filter; the digital tuning engineexecutes a filter mismatch calibration to match the I-path analog filterand the Q-path analog filter; and the digital tuning engine executes afilter residual mismatch calibration to match an I-path response fromthe I-path analog filter to the digital compensation circuit and aQ-path response from the Q-path analog filter to the digitalcompensation circuit.
 2. The RF receiver according to claim 1, wherein:the I-path analog filter includes a plurality of capacitors eachincluding a capacitor bank tuned by the digital tuning engine; and theQ-path analog filter includes a plurality of capacitors each including acapacitor bank tuned by the digital tuning engine.
 3. The RF receiveraccording to claim 2, wherein: the capacitor bank includes a pluralityof parallel sub-capacitors and a plurality of parallel switches, andeach switch serially connects to a corresponding one of thesub-capacitors; and the digital tuning engine controls setting of thecapacitor bank by turning on/off of the switches of the capacitor bank.4. The RF receiver according to claim 2, wherein: in executing the RCtime constant calibration, the digital tuning engine gets a capacitorbank setting by performing RC time constant calibration on one of thecapacitors of either the I-path analog filter or the Q-path analogfilter; and the digital tuning engine tunes all of the capacitors ofboth the I-path analog filter and the Q-path analog filter based on thecapacitor bank setting.
 5. The RF receiver according to claim 2,wherein: in executing the RC time constant calibration, the digitaltuning engine gets an I-path capacitor bank setting by performing RCtime constant calibration on one of the capacitors of the I-path analogfilter; and the digital tuning engine tunes all of the capacitors of theI-path analog filter based on the I-path capacitor bank setting.
 6. TheRF receiver according to claim 2, wherein: in executing the RC timeconstant calibration, the digital tuning engine gets a Q-path capacitorbank setting by performing RC time constant calibration on one of thecapacitors of the Q-path analog filter; and the digital tuning enginetunes all of the capacitors of the Q-path analog filter based on theQ-path capacitor bank setting.
 7. The RF receiver according to claim 2,wherein: in executing the filter mismatch calibration, the digitaltuning engine gets I/Q gain and phase imbalances at two distinctfrequencies to mach the I-path analog filter and the Q-path analogfilter.
 8. The RF receiver according to claim 7, further comprising twomixers respectively in front of and respectively coupled to the I-pathanalog filter and the Q-path analog filter; wherein: in response to afirst tone at an in-band frequency in front of the mixers, the digitaltuning engine gets a first I/Q gain imbalance and a first I/Q phaseimbalance at the in-band frequency; in response to a second tone at anear-cut-off frequency or at a certain frequency in front of the mixers,the digital tuning engine gets a second I/Q gain imbalance and a secondI/Q phase imbalance at the near-cut-off frequency or at the certainfrequency; the digital tuning engine tunes settings of the capacitorbanks of the I-path analog filter and/or the Q-path analog filter basedon a first difference between the first I/Q gain imbalance and thesecond I/Q gain imbalance; and the digital tuning engine tunes settingsof the capacitor banks of the I-path analog filter and/or the Q-pathanalog filter based on a second difference between the first I/Q phaseimbalance and the second I/Q phase imbalance.
 9. The RF receiveraccording to claim 7, further comprising two mixers respectively infront of and respectively coupled to the I-path analog filter and theQ-path analog filter; wherein: in response to at least one third tone atan in-band frequency in front of the mixers, the digital tuning enginegets a third I/Q gain imbalance and a third I/Q phase imbalance at thein-band frequency; in response to at least one fourth tone at anear-cut-off frequency or at a certain frequency in front of the mixers,the digital tuning engine gets a fourth I/Q gain imbalance and a fourthI/Q phase imbalance at the near-cut-off frequency or at the certainfrequency; the digital tuning engine tunes settings of the capacitorbanks of the I-path analog filter and/or the Q-path analog filter basedon a third difference between the third I/Q gain imbalance and thefourth I/Q gain imbalance; and the digital tuning engine tunes settingsof the capacitor banks of the I-path analog filter and/or the Q-pathanalog filter based on a fourth difference between the third I/Q phaseimbalance and the fourth I/Q phase imbalance.
 10. The RF receiveraccording to claim 7, wherein: in response to a fifth tone at an in-bandfrequency in front of the I-path analog filter and the Q-path analogfilter, the digital tuning engine gets a fifth I/Q gain imbalance and afifth I/Q phase imbalance at the in-band frequency; in response to asixth tone at a near-cut-off frequency or at a certain frequency infront of the I-path analog filter and the Q-path analog filter, thedigital tuning engine gets a sixth I/Q gain imbalance and a sixth I/Qphase imbalance at the near-cut-off frequency or at the certainfrequency; the digital tuning engine tunes settings of the capacitorbanks of the I-path analog filter and/or the Q-path analog filter basedon a fifth difference between the fifth I/Q gain imbalance and the sixthI/Q gain imbalance; and the digital tuning engine tunes settings of thecapacitor banks of the I-path analog filter and/or the Q-path analogfilter based on a sixth difference between the fifth I/Q phase imbalanceand the sixth I/Q phase imbalance.
 11. The RF receiver according toclaim 7, wherein: in response to at least one seventh tone at an in-bandfrequency in front of the I-path analog filter and the Q-path analogfilter, the digital tuning engine gets a seventh I/Q gain imbalance anda seventh I/Q phase imbalance at the in-band frequency; in response toat least one eighth tone at a near-cut-off frequency or at a certainfrequency in front of the I-path analog filter and the Q-path analogfilter, the digital tuning engine gets a eighth I/Q gain imbalance and aeighth I/Q phase imbalance at the near-cut-off frequency or at thecertain frequency; the digital tuning engine tunes settings of thecapacitor banks of the I-path analog filter and/or the Q-path analogfilter based on a seventh difference between the seventh I/Q gainimbalance and the eighth I/Q gain imbalance; and the digital tuningengine tunes settings of the capacitor banks of the I-path analog filterand/or the Q-path analog filter based on a eighth difference between theseventh I/Q phase imbalance and the eighth I/Q phase imbalance.
 12. Adigitally-assisted calibration method applicable to a radio frequency(RF) receiver including an I (in-phase)-path analog filter, a Q(quadrature-phase)-path analog filter and a digital compensationcircuit, the method comprising: executing a RC (resistor-capacitor) timeconstant calibration to adjust respective cut-off frequencies of theI-path analog filter and the Q-path analog filter; executing a filtermismatch calibration to match the I-path analog filter and the Q-pathanalog filter; and executing a filter residual mismatch calibration tomatch an I-path response from the I-path analog filter to the digitalcompensation circuit and a Q-path response from the Q-path analog filterto the digital compensation circuit.
 13. The digitally-assistedcalibration method according to claim 12, wherein: in executing the RCtime constant calibration, getting a capacitor bank setting by using oneof capacitors of either the I-path analog filter or the Q-path analogfilter; and tuning all of the capacitors of both the I-path analogfilter and the Q-path analog filter based on the capacitor bank setting.14. The digitally-assisted calibration method according to claim 12,wherein the step of executing the RC time constant calibration includes:getting an I-path capacitor bank setting by using one of capacitors ofthe I-path analog filter; and tuning all of the capacitors of the I-pathanalog filter based on the I-path capacitor bank setting.
 15. Thedigitally-assisted calibration method according to claim 12, wherein thestep of executing the RC time constant calibration includes: getting aQ-path capacitor bank setting by using one of the capacitors of theQ-path analog filter; and the digital tuning engine tunes all of thecapacitors of the Q-path analog filter based on the Q-path capacitorbank setting.
 16. The digitally-assisted calibration method according toclaim 12, wherein the step of executing the filter mismatch calibrationincludes: getting I/Q gain and phase imbalances at two distinctfrequencies to match the I-path analog filter and the Q-path analogfilter.
 17. The digitally-assisted calibration method according to claim16, wherein: the RF receiver further comprises two mixers respectivelyin front of and respectively coupled to the I-path analog filter and theQ-path analog filter; the step of executing the filter mismatchcalibration includes: in response to a first tone at an in-bandfrequency in front of the mixers, getting a first I/Q gain imbalance anda first I/Q phase imbalance at the in-band frequency; in response to asecond tone at a near-cut-off frequency or at a certain frequency infront of the mixers, getting a second I/Q gain imbalance and a secondI/Q phase imbalance at the near-cut-off frequency or at the certainfrequency; tuning settings of the capacitor banks of the I-path analogfilter and/or the Q-path analog filter based on a first differencebetween the first I/Q gain imbalance and the second I/Q gain imbalance;and tuning settings of the capacitor banks of the I-path analog filterand/or the Q-path analog filter based on a second difference between thefirst I/Q phase imbalance and the second I/Q phase imbalance.
 18. Thedigitally-assisted calibration method according to claim 16, wherein theRF receiver further comprises two mixers respectively in front of andrespectively coupled to the I-path analog filter and the Q-path analogfilter; the step of executing the filter mismatch calibration includes:in response to at least one third tone at an in-band frequency in frontof the mixers, getting a third I/Q gain imbalance and a third I/Q phaseimbalance at the in-band frequency; in response to at least one fourthtone at a near-cut-off frequency or at a certain frequency in front ofthe mixers, getting a fourth I/Q gain imbalance and a fourth I/Q phaseimbalance at the near-cut-off frequency or at the certain frequency;tuning settings of the capacitor banks of the I-path analog filterand/or the Q-path analog filter based on a third difference between thethird I/Q gain imbalance and the fourth I/Q gain imbalance; and tuningsettings of the capacitor banks of the I-path analog filter and/or theQ-path analog filter based on a fourth difference between the third I/Qphase imbalance and the fourth I/Q phase imbalance.
 19. Thedigitally-assisted calibration method according to claim 16, wherein thestep of executing the filter mismatch calibration includes: in responseto a fifth tone at an in-band frequency in front of the I-path analogfilter and the Q-path analog filter, getting a fifth I/Q gain imbalanceand a fifth I/Q phase imbalance at the in-band frequency; in response toa sixth tone at a near-cut-off frequency or at a certain frequency infront of the I-path analog filter and the Q-path analog filter, gettinga sixth I/Q gain imbalance and a sixth I/Q phase imbalance at thenear-cut-off frequency or at the certain frequency; tuning settings ofthe capacitor banks of the I-path analog filter and/or the Q-path analogfilter based on a fifth difference between the fifth I/Q gain imbalanceand the sixth I/Q gain imbalance; and tuning settings of the capacitorbanks of the I-path analog filter and/or the Q-path analog filter basedon a sixth difference between the fifth I/Q phase imbalance and thesixth I/Q phase imbalance.
 20. The digitally-assisted calibration methodaccording to claim 16, wherein the step of executing the filter mismatchcalibration includes: in response to at least one seventh tone at anin-band frequency in front of the I-path analog filter and the Q-pathanalog filter, getting a seventh I/Q gain imbalance and a seventh I/Qphase imbalance at the in-band frequency; in response to at least oneeighth tone at a near-cut-off frequency or at a certain frequency infront of the I-path analog filter and the Q-path analog filter, gettinga eighth I/Q gain imbalance and a eighth I/Q phase imbalance at thenear-cut-off frequency or at the certain frequency; tuning settings ofthe capacitor banks of the I-path analog filter and/or the Q-path analogfilter based on a seventh difference between the seventh I/Q gainimbalance and the eighth I/Q gain imbalance; and tuning settings of thecapacitor banks of the I-path analog filter and/or the Q-path analogfilter based on a eighth difference between the seventh I/Q phaseimbalance and the eighth I/Q phase imbalance.